Nice. I've seen those at Performance and such. In my case, I've always had mountain bikes, and I'm not sure how they'd work with it...seems like you'd need slicker tires for the thing to work right. But the concept is good!
It does cost more than $20, though. I'm really thinkin' I might as well give that thing a shot. Could certainly resell it for the same if'n it doesn't work out. I never regretted my last cheap exercise equipment purchase - that treadmill I had until I moved.
We have a hybrid 21 speed we use with it... knobby tires...
It was an investment, to be sure, but this is the only real heavy cardio my body can take... runnin' wrecks whats left of my knees, hips, and back... I peddle till I puke on this for 45-60 minutes, and I feel great...
The money I've saved the past two years on good running shoes has more than paid for it...